1. Field of the Invention
The invention relates to the use of a disc-shaped rotary cutter for excavating hard mineral rock layers.
2. Description of the Related Art
DE-OS [German Unexamined Published Patent Application] 3,822,200 discloses a method of excavating limestone (marl) in which the limestone is produced directly in small sized grains in one process phase during the excavation in essentially a grain size that can be transported on a conveyor belt. The preferred excavator employed is a bucket wheel excavator. Although bucket wheel excavators are now available that can be used in harder rock layers, their performance is limited if they are of conventional configuration, particularly when considering the wear that occurs at the cutting elements. Beginning with a certain rock hardness, conventional methods must be employed, such as drilling, blasting, excavation by a mechanical shovel, loading onto trucks or transporting by rail, breaking up the essential limestone component as well as transporting it further on conveyor belt systems. The multitude of process steps performed from excavation to conveyor belt transport results not only in great delays but also in a relatively small throughput with high costs for materials and personnel. Due to the blasting, the material remains in large pieces and must be almost all fed into a crusher before it can be transported further.
East German Patent 10,487 discloses an excavator for digging small trenches by cutting blades that are disposed at blade supports of a pivotal wheel disc and guide rings that are provided on both sides of the cutting blades. The blade holders and the cutting blades are alternatingly fastened to one side of the blade supports. This type of excavator, which is also known as a trench cutting machine, is provided exclusively to produce trenches of a relatively small width and depth (depending on the diameter), with generally no hard rock layers being involved, but rather loose soil or clay, so that no high demands are made with respect to wear of the cutting elements.